Beam landing error control apparatus for magnetically focused cathode ray tubes

ABSTRACT

In magnetically focused electron beam tubes transverse velocity components of the beam are introduced by the electrostatic or electromagnetic fields of the beam deflection components. By providing a pair of beam deflection components and spacing them substantially one-half focus loop length of the electron beam along the tube axis, a transverse velocity component introduced by one beam deflection component is canceled or enhanced by a transverse velocity component introduced by the other beam deflection component.

States atent Inventor Roy A. Minet Lancaster, Pa. Appl. No. 712.978 Filed Mar. 14, 1968 Patented Jan. 26, 1971 Assignee RCA Corporation a corporation of Delaware BEAM LANDING ERROR CONTROL APPARATUS FOR MAGNETICALLY FOCUSED CATHODE RAY TUBES Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-Eugene M. Whitacre ABSTRACT: In magnetically focused electron beam tubes transverse velocity components of the beam are introduced by 12 Chums 8 Drawing the electrostatic or electromagnetic fields of the beam deflec- US. Cl 313/76, tion components. By providing a pair of beam deflection com- 315/10 ponents and spacing them substantially one-half focus loop Int. Cl ..H0lj 29/70, length of the electron beam along the tube axis, a transverse HOlj 31/26 velocity component introduced by one beam deflection com- Field of Search 313/76, 77, ponent is canceled or enhanced by a transverse velocity com- 84, 83 ponent introduced by the other beam deflection component.

9M +1012 +412V. ,8 j l6 z7+4iuvz Z6 +57!v 22 J7" I I: 1 I 1 "3% i; i I: 46 ri a La s 14 3 6 '54 (25M 25 ATENTEU JAMES I971 After/mg BEAM LANDING ERROR CONTROL APPARATUS FOR MAGNETICALLY FOCUSED CATIIODE RAY TUBES BACKGROUND OF THE INVENTION This invention relates to apparatus for controlling the alignment, deflection, and steering of electron beams in cathode ray tubes utilizing magnetic focusing.

Various types of cathode ray pickup tubes including the image orthicon and the isocon have been developed for use in electronic cameras such as television cameras, for example, In these types of tubes electrons emitted from a cathode are formed into a beam and are accelerated by the electrodes within the tube towards a target. The beam is focused by a magnetic field extending along the longitudinal axis of the tube between the cathode'and the target and it is along this axis that the electron beam is directed.

Alignment coils have been used to produce lines of flux to interact with the focusing field so as to introduce transverse velocity components to control the character of the beam. Deflection coils have been used to introduce transverse velocity components to deflect the beam over the surface of the target for scanning purposes. In addition, electrostatic deflection plates have been used to introduce transverse velocity components to provide a vernier deflection adjustment.

As the electrons in the beam are accelerated towards the target, they are subjected to the transverse fields provided by the alignment and deflection coils and the deflection plates as well as the axial magnetic field provided by the focusing magnet. The interaction of these fields and the electron beam causes electrons comprising the beam to travel in a helical rather than a straight path. Each electron in the beam passes through the longitudinal beam axis once for every 360 of its helical travel. The points at which the electrons cross the beam axis are called focus nodes. The points at which the electrons are furthest from the beam axis are called antinodes. The accelerating potentials and the magnetic fields are selected such that the beam is at a focus node as it reaches the target. The target is in a plane perpendicular to the longitudinal axis of the tube. In operation the target is charged positively with respect to the cathode, the amount of charge being related to the signal strength of an image formed by light rays on the photocathode faceplate of the tube. The target is scanned by the primary electron beam. Among the problems encountered in the operation of the tube is the interaction of the various magnetic fields within the tube and the resulting landing error caused by this interaction.

Landing errors are the time-varying transverse velocity components of the beam, at the point of impact with the target. Landing error results in the beam striking the target at varying angles during scanning. The return electron beam comprises scattered electrons and specularly reflected electrons. The specularly reflected electron portion of the beam contains the electrons of the original beam which retain their transverse velocity components. The scattered electron portion of the return beam contains electrons released from the target in response to bombardment by the original beam and may be regarded as not having any particular transverse velocity component. In image isocons the image information is contained in the scattered electron portion of the beam.

In orthicons, landing error is seen as a variations in the black-to-white signal as a function of the location of the beam in the raster. In beam separation tubes, such as the isocon, this same effect is observed and, in addition, gray scale, signal to noise ratios and black level may vary across the raster.

Various methods of correcting landing errors are possible. The focus field can be made to vary along the tube axis or dynamic modulation of the alignment coils with various waveforms may be employed. Also, the deflection coils can be segmented and the segments operated with identical or different waveforms.

SUMMARY OFTHE INVENTION In a cathode ray tube having a magnetically focused elec tron beam first and second electron beam deflection means are disposed along the beam trajectory and are spaced apart substantially an odd multiple of one-half the focus loop length of the beam. The first and second electron beam deflection means produce beam deflection fields so that a transverse component of velocity imparted to the beam by the action of the field produced by the first deflection means is either enhanced or opposed by a transverse component of velocity imparted by the second beam deflection means.

It is an object of this invention to provide apparatus for deflecting a magnetically focused electron beam without thereby imparting a transverse component of velocity to the beam.

It is another object of this invention to provide apparatus for imparting a transverse component of velocity to a magnetically focused electron beam without deflecting it.

The invention is more fully described in the following specification taken in conjunction with the accompanying drawings in which:

FIG. I is a longitudinal sectional view ofa television camera tube including electron beam control apparatus embodying the invention;

FIG. 2 is a longitudinal sectional view, partly broken away. of a camera tube including alignment coils in accordance with the invention;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along the line 4-4 ofFIG. 2;

FIG. Sis a sectional view taken along the line 5-5 ofFlG. 1;

FIG. 6 is a sectional view taken along the line 66 ofFlG. 6',

FIG. 7 is a sectional view taken along the line 77 of FIG. I; and

FIG. 8 is a sectional view taken along the line 8-8 of FIG. 1.

DESCRIPTION FIG. 1 shows a portion ofa television camera 10 comprising a photoemissive pickup tube 12, a lens 14 and a coil system. The coil system includes focusing coil I6, alignment coil 22 and its opposite member 220, and, in accordance with the present invention, alignment coils 24 and 26 and their respective opposite members 23 and 25, and deflection coils 18, I9, 20 and 21. Also in accordance with the present invention, steering plates 27, 28, 29 and 30 are shown. Alignment plates 15 and 17 are also shown.

The tube 12 with the exception of the steering plates is similar to an image isocon of the type described in U. S. Pat. application Ser. No. 629,129, filed Apr. 7, I967, entitled Television Camera Including an Image Isocon Tube and which is now U. S. Pat. No. 3,471,74l issued Oct. 7, I969. The tube 12 comprises an elongated glass envelope 31 having an electron gun 32 and an electron multiplier 34 positioned in one end portion thereof. The electron gun 32 includes a cathode 38 and a beam-forming aperture plate 36 having a relatively small opening of about 0.002 inch diameter. The components of the electron gun and multiplier may be of any suitable construction.

Electrode 54 is a conductive coating on the inside wall of the glass envelope 31 and establishes a uniform electrostatic potential around the inside of the glass envelope when connected to a source of potential by an electrode, not shown.

The tube 12 at its other end terminates in a glass faceplate 40 having one the inner surface thereof a conventional semitransparent photocathode 42 comprising, for example, a commercially available 5-10 photocathode.

Spaced from the photocathode 42 is a storage target 44, which may comprise any conventional structure such as a thin membrane of glass, magnesium oxide or aluminum oxide, supported in a conventional manner. A decelerator mesh screen 46 is closely spaced, 0.2 inches for example, from the gun side of the storage target 44. A secondary electron mesh screen 48 is closely spaced, 0.001 inch for example, from the photocathode side of the storage target 44. Photoemission from the photocathode 42 forms an electrostatic image on the target 44 which corresponds to a light image focused on the photocathode 42 by the lens 14. In view of the thinness of the target 44 the electrostatic image formed thereon appears on both sides of the target. For focusing the image information in the photoelectron emission from the photocathode 42 upon the target 44, focusing means are provided such as a metal ring electrode 50 adjacent to the photocathode 42 and a metal cylindrical electrode 52 supporting the mesh screen 48 and the target 44.

During operation, the cathode 38 of the electron gun 32 may be grounded and tube elements such as the photocathode 42, the mesh screen 46, the electrode 50, the electrode 52 and the electrode 54, may be impressed with the potentials shown in FIG. 1. The electron beam 56 from the electron gun 32 passes through the mesh screen 46 and is decelerated to a few volts of energy as it approaches the target 44. The decelerated beam 56 is scanned across the surface of the target 44 facing the electron gun 32 by the deflection coils 18, 19, and 21, and establishes a stable potential on the gun side of the target 44 that is relatively close to the potential of the cathode. Any change in the stable potential, such as that produced by an electron charge pattern from the photocathode 42 corresponding to a light image focused on the photocathode by the lens 14, will be sensed by the scanning beam 56. The sensing is accomplished by a different, response of the beam to noncharged regions of the target from that of regions charged substantially above cathode potential. Such response modifies the character ofthe return beam.

The return beam from the noncharged regionsconsists solely of specularly reflected electrons. The return beam from charged regions of the target consists of two parts. One part comprises specularly reflected electrons 60 and the other part comprises scattered electrons 57. The scattered electrons are distributed throughout the cross-sectional area of the beam at a focus antinode. The specularly reflected electrons are concentrated in a relatively small area of this beam cross section, but off the beam axis. The scattered electrons are characterized by a range of velocities that is different from that of the specularly reflected electrons. The specularly reflected electrons and the scattered electrons, by virtue of their different velocities, will assume the different locations in the return beam described above. Thus, as shown schematically in FIG. 1, a first portion 60 of the return beam is formed by specularly reflected electrons while a second portion 57 is constituted of scattered electrons. The scattered electrons forming return beam portion 57 are employed in the isocon as the signal electrons representative of the electrostatic image formed on target 44. A persuader electrode 66 having an aperture 67 is provided and is connected to a suitable potential source for urging the scattered electrons toward the electron multiplier 34.

Alignment coils 22, 24, and 26, and their respective opposite members 21, 23 and 25, are positioned around the outside of the glass envelope 31 at the electron gun end portion of the tube. Alignment coils 22a and 22 produce a transverse magnetic field across the tube to impart a transverse velocity to the electron beam. The alignment coil 22-22a field and the axial focusing field interact with the electron beam to cause the beam to follow a helical trajectory. A pair of alignment plates 15 and 17 are positioned along the beam path between the cathode 38 and the beam limiting aperture plate 36.

Deflection coils 18, 19, 20 and 21 are positioned around the outside of the glass envelope 31 at a location between the target 44 and the steering plates 27, 28, 29 and 30. For illustration, only the horizontal deflection coils are shown, but it is to be understood that there are actually another set of four coils for vertical deflection. The arrangement of each of the vertical and horizontal sets of coils is similar, but displaced by 90.

Steering plates 27 and 28 are connected together electrically. Steering plates 29 and 30 also are connected together electrically. Each pair of plates 27 and 28, and 29 and 30, is adapted to be connected to a power supply, not shown, so that an electric field is established between the sets of plates. The plates are supported within the glass envelope 31 in a conventional manner. For illustration, only two pairs of steering plates are shown, but it is to be understood that four additional plates similarly connected together and connected to separate sources of potential, are disposed annularly within the tube 90 from the plates 27, 28, 29 and 30 such that a second electric field is established which is at right angles to the field established between plates 27 and 28, and 29 and 30. The separate fields combine and produce a resultant electric field of predetermined magnitude and direction.

The alignment coils 24 and 26, and their respective opposite members 23 and 25, provide magnetic fields which further align the beam. This alignment supplements the alignment provided by alignment coil 22. The deflection coils l8 and 20, and their respective opposite members 19 and 21, provide transverse magnetic fields which causes the electron beam to scan the target 44.

The electric field of steering plates 27, 28, 29 and 30, displace the primary and return beams such that specularly reflected electrons 60 pass through the aperture 64 in separating plate 62. The scattered electrons are intercepted by separating plate 62 and are accelerated into the electron multiplier 34.

The distance along the tube axis between adjacent focus nodes is 2 focus loop length. Each focus loop contains a focus node 53 and a focus antinode 55. The distance between the focus nodes is primarily established by the focus field. The term alignmenf' as applied to coils 22a-26 may be somewhat misleading in the sense that these coils do not align the electron beam with respect to the tube axis, but rather, impart a transverse velocity component to the electrons in the beam. The amount of the transverse velocity component of the beam, combining with the focusing field establishes the shape of the beam trajectory. The current in alignment coils 22a and 22 is adjusted for maximum signal, which corresponds to maximum beam current through the aperture 64, for a given fixed field between alignment plates 15 and 17.

Referring now to FIG. 2, the center of alignment coils 26 and 25 are shown spaced a distance d from the center of alignment coils 24 and 23. The distance d is substantially equal to one-half the focus loop length of the electron beam 56. Coils 24 and 23 are wound such that a transverse magnetic field, represented by the arrows 41, is produced and is in the direction indicated by the arrows. Coils 26 and 25 are wound such that a magnetic field, represented by the arrows 43, is produced with the flux lines in the opposite direction from the flux lines of magnetic field 41. The ampere turns of each of the coils 24 and 23, and 26 and 25 are adjusted such that a source of direct current (not shown) will produce the equal and opposite magnetic fields 41 and 43 when connected to the windings of the coils.

As indicated in FIG. 3, the circle 53 is the end view of the helix formed by the electrons in the beam. For illustrating the invention, the effect of the coils on only a single electron 51 of the electron beam 56 will be described. It is understood that all of the electrons in the beam will be similarly affected. The magnetic field 41 causes a transverse velocity component V 0 the electron 51 as indicated by the arrow.

As shown in FIG. 2, magnetic field 43 produced by the coils 26 and 25 are opposite those produced by the magnetic field 41 of coils 24 and 23, Coils 26 and 25 are spaced substantially one-half the focus loop length of the electron beam from coils 24 and 23. During the time it takes the electron 51 to travel this distance the electron also travels l from the position shown in FIG. 3 to that shown in FIG. 4. The velocity vector V rotates with electron 51. The magnetic field 43 adds a transverse velocity component V to the electron Sll. Velocity component V is thus added to V and the change of alignment is a function of V and V The net deflection component of the beam produced by the magnetic field 41 in FIG. 3 is canceled by an equal and opposite net deflection component produced by magnetic field 43 in FIG. 4. The net effect of coils 24 and 23 and 26 and 25 on the beam passing through the coils is to change the alignment (i.e., the transverse velocity component of the beam) without a change in deflection of the beam. The return beam will be subjected to forces opposite those shown in FIGS. 3 and 4. These forces will again change the alignment of the beam with no net deflection component introduced. The magnitude and direction of the forces are adjusted to align the beam in a predetermined manner.

As previously described, alignment coils 24 and 26, and their respective opposite members, supplement the alignment imparted to the beam by coils 22a and 22 and alignment plates and 17. The tube may be operated without coils 2324 and 25-26 if coils 22-2211 and alignment plates 15 and 17 are usedfor' alignment. Coils Hand 22 and'alignment plates 15 and 17 are used to position the beam such that it passes through the aperture 64 of separating electrode 62.

Referring again to FIG. 1, it is shown that the deflection coils l8 and 20, and their respective opposite members 19 and 21, are offset from each other a distance a substantially equal one-half a focus loop length of the electron beam. Coils 18 and 19, and 20 and 21 are wound in series such that when energized by a source of sawtooth current (not shown) produce transverse magnetic fields 47 and 33, respectively. Magnetic fields 47 and 33 are in the same direction and are of substantially equal magnitude.

Magnetic fields 47 and 33 combine with the axial magnetic field produced by focusing electromagnet l6 and form a resultant magnetic field.

Referring now to FIG. 5, the effects of the magnetic field 33 and the focusing field are shown on an electron 51 of the beam as it arrives at the target 44. The beam has been displaced a distance B, represented as the distance between the center axis R of the tube and the center axis S of the beam, by the resultant of the two fields. Additionally, a net transverse velocity component, represented by the vector V has been produced at the target 44 by the resultant of the two fields.

Referring now to FIG. 6, the effects of the magnetic field 47 and the focusing field are shown on an electron 51 ofthe beam as it arrives at the target 44. The beam has been deflected a greater distance for a total deflection B as represented by the distance between the center axis R of the tube and the center axis S of the beam. Additionally, the net effect of the two fields is to produce a transverse velocity component at the target 44, represented by the vector V,, which is substantially equal and opposite to the component V Therefore, the trans verse velocity components produced by each pair of deflection coils 18 and 19, and 20 and 21, are canceled. In this manner the electron beam has been displaced without a net transverse velocity component, with the result that the landing error is greatly reduced.

Referring again to FIG. 1, it is shown that steering plates 27 and 29 are spaced a distance d from plates 28 and 30, respec tively. Distance d is substantially equal to one-half the focus loop length of electron beam 56. An electric field, indicated by the arrows 35, is produced between the plates 28 and 30. An electric field, indicated by the arrows 37, is produced between the plates 27 and 29. Electric fields 35 and 37 are in the same direction and are of substantially equal magnitude.

Referring now to FIG. 7, the combined effects produced by electric field 35 and the focusing field, on the electron 51 of the beam as it arrives at the target 44 are shown by the vector V which is a transverse velocity component. The beam has been displaced a distance C, represented as the distance between the center axis R of the tube and the center axis S of the electron beam.

Referring now to FIG. 8, the combined effects produced by electric field 37 and the focusing field, on the electron 51 of the beam as it arrives at the target 44 are shown. The beam has been displaced an additional distance for a total displacement C between the center axis R of the tube and the center axis 5 of the electron beam. Another net effect is a transverse velocity component represented by vector V V is substantially equal and opposite V Therefore, the separate transverse velocity components produced by the pairs of steering plates 27 and 29, and 28 and 30, cancel. In this manner the electron beam has been steered without introduction of a net transverse velocity component. The return beam in passing through the plates receives an additional displacement in the same direction and equal in magnitude to C, and no net transverse velocity component is introduced. The potentials applied to the steering plates 27 and 28, and 29 and 30. respectively, are selected such that the return beam is steered into a position at which the scattered electron 6O strike the separating electrode 62 and are accelerated into electron multiplier 34, and the specularly reflected electrons 57 pass through the aperture 64 ofthe separating electrode 62 and are discarded.

ln'another embodiment of the invention. not shown, an

electric field may be established between the plates 27 and 29 which is opposite in direction to the field between the plates 28 and 30, and the two pairs of plates are disposed an odd multiple of substantially one-quarter focus loop length along the longitudinal axis of the tube from the focus node at the target. In this manner, a transverse velocity component is added to the primary beam and an opposite transverse velocity com ponent added to the return beam. The result is no net trans verse velocity component and no net deflection added to the specularly reflected electrons. The scattered electrons of the return beam are subjected to the one-way net transverse velocity change introduced by the two pairs of plates con nccted as previously stated. In this manner. it is possible to control the alignment of the primary beam without affecting the alignment or displacement of the specularly reflected portion of the return beam.

lclaim: 1. An electron beam control apparatus for cathode ray tubes comprising:

means providing a magnetic focusing field for said electron beam causing said beam to define focus nodes and antinodes, in its trajectory in said cathode ray tube; first deflection'means disposed along the trajectory of said electron beam; and second deflection means disposed along the trajectory of said electron beam, said first deflection means displaced with respect to said second deflection means displaced with respect to said second deflection means along said trajectory by a distance substantially equal to an odd mul tiple, including one, of the distance between a focus node and an adjacent focus antinode. 2. Electron beam control apparatus for cathode ray tubes comprising:

means providing a magnetic focusing field extending along the trajectory of said electron beam; first deflection means disposed adjacent the trajectory of said beam for imparting a first transverse velocity component to said beam and for producing a first deflecting field; and second deflection means disposed adjacent the trajectory of said beam for producing a second deflecting field in the same direction as said first deflecting field, said second deflection means being disposed along said trajectory from said first deflection means a distance substantially equal to an odd multiple, including one, of one-half a focus loop length of said beam for imparting a second transverse velocity component to said beam, said second transverse velocity component being in an opposite direction from said first transverse velocity component. 3. Electron beam control apparatus for cathode ray tubes comprising:

means providing a magnetic focusing field extending along the trajectory of said electron beam; first deflection means adjacent the trajectory of said beam for imparting a transverse velocity component to said beam, said first deflection means producing a deflecting field in a first direction transverse to said focusing field; and

second deflection means adjacent the trajectory of said beam, said second deflection means producing a deflecting field in the opposite direction to that produced by said first deflection means and displaced from said first deflection means by a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode so to impart a transverse velocity component to said beam in the same direction as the transverse velocity component imparted to said beam by said first deflection means.

4. Electron beam control apparatus for cathode ray tubes comprising:

means providing a magnetic focusing field extending along the longitudinal axis of said tube, said focusing field causing said beam to form focus nodes and antinodes in its trajectory;

first deflection means disposed along said longitudinal axis of said tube for imparting a first net deflection and a first net transverse velocity component to said beam transverse to said focusing field;

second deflection means disposed along said longitudinal axis displaced from said first deflection means a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode for imparting a second net deflection and a second net transverse velocity component to said beam transverse to said focusing field; and

said first and second net deflections being in the same direction and said first and second net transverse velocity components being in opposite directions.

5. Electron beam control apparatus for cathode ray tubes comprising:

means providing a magnetic focusing field extending along the longitudinal axis of said tube, said focusing field causing said beam to form focus nodes and antinodes in its trajectory;

first deflection means disposed along said longitudinal axis of said tube for imparting a first net deflection and a first net transverse velocity component to said beam transverse to said focusing;

second deflection means disposed along said longitudinal axis displaced from said first deflection means a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode for imparting a second net deflection and a second net transverse velocity component to said beam transverse to said focusing field; and

said first and second net deflections being in opposite directions and said first and second net transverse velocity components being in the same direction.

6. Electron beam control apparatus for cathode ray tubes according to claim 4 wherein:

said first deflection means includes at least one deflection electromagnet; and said second deflection means includes at least one deflee tion eleetromagnet. 7. Electron beam control apparatus for cathode ray tubes according to claim 4 wherein:

said first deflection means includes at least two electrostatic deflection plates; and said second deflection means includes at least two electrostatic deflection plates. 8. Electron beam control apparatus for cathode ray tubes according to claim 5 wherein:

said first deflection means includes at least one alignment electromagnet; and said second deflection means includes at least one alignment electromagnet. 9. Electron beam control apparatus for cathode ray tubes according to claim 6 wherein:

said first and second net deflections are of substantially equal magnitude; and said first and second'net transverse velocity components are of substantially equal magnitude. 10. Electron beam control apparatus for cathode ray tubes according to claim 7, wherein:

said first and second net deflections are of substantially equal magnitude; and said first and second net transverse velocity components are of substantially equal magnitude. 11. Electron beam control apparatus for cathode ray tubes according to claim 8, wherein:

said first and second net deflections are of substantially equal magnitude; and said first and second net transverse velocity components are of substantially equal magnitude. 12. A method of controlling the deflection ofa magnetically focused electron beam in a cathode ray tube comprising:

imparting a first net force to said electron beam over a first portion of its trajectory, said first force producing a first net deflection component and a first net transverse velocity component on said beam; imparting a second force to said electron beam over a second portion of its trajectory, said second force producing a second net deflection component and a second net transverse velocity component on said beam; and said first and second portions of said trajectory being displaced a distance equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode of said beam.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 558, 953 Dated January 26, 1971 lnventor(s) Roy A. Minet It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 26, that portion reading "2 focus loop lengi should read a focus loop length line 60, that portic reading "0 the electron" should read to the electron Column 7, line 20, that portion reading "focusing field; should read 'focusing field; and line 27, that portir reading "focusing field; and" should read focusing fiel( line 41, that portion reading "said focusing;" should read said focusing; and line 48, that portion reading "focusing field; and" should read focusing field; Column 8, line 42, that portion reading "on said beam; should read on said beam; and line 46, that portion reading "on said beam; and" should read on said beam;

Signed and sealed this 29th day of June 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER Attesting Officer Commissioner of Patn FORM PO-105O (lo-s91 USCOMM Dc Q U 5 GOVFRNMENY PRINTING OFFICI 1 I!!! 

1. An electron beam control apparatus for cathode ray tubes comprising: means providing a magnetic focusing field for said electron beam causing said beam to define focus nodes and antinodes, in its trajectory in said cathode ray tube; first deflection means disposed along the trajectory of said electron beam; and second deflection means disposed along the trajectory of said electron beam, said first deflection means displaced with respect to said second deflection means displaced with respect to said second deflection means along said trajectory by a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode.
 2. Electron beam control apparatus for cathode ray tubes comprising: means providing a magnetic focusing field extending along the trajectory of said electron beam; first deflection means disposed adjacent the trajectory of said beam for imparting a first transverse velocity component to said beam and for producing a first deflecting field; and second deflection means disposed adjacent the trajectory of said beam for producing a second deflecting field in the same direction as said first deflecting field, said second deflection means being disposed along said trajectory from said first deflection means a distance substantially equal to an odd multiple, including one, of one-half a focus loop length of said beam for imparting a second transverse velocity component to said beam, said second transverse velocity component being in an opposite direction from said first transverse velocity component.
 3. Electron beam control apparatus for cathode ray tubes comprising: means providing a magnetic focusing field extending along the trajectory of said electron beam; first deflection means adjacent the trajectory of said beam for imparting a transverse velocity component to said beam, said first deflection means producing a deflecting field in a first direction transverse to said focusing field; and second deflection means adjacent the trajectory of said beam, said second deflection means producing a deflecting field in the opposite direction to that produced by said first deflection means and displaced from said first deflection means by a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode so as to impart a transverse velocity component to said beam in the same direction as the transverse velocity component imparted to said beam by said first deflection means.
 4. Electron beam control apparatus for cathode ray tubes comprising: means providing a magnetic focusing field extending along the longitudinal axis of said tube, said focusing field causing said beam to form focus nodes and antinodes in its trajectory; first deflection means disposed along said longitudinal axis of said tube for imparting a first net deflection and a first net transverse velocity component to said beam transverse to said focusing field; second deflection means disposed along said longitudinal axis displaced from said first deflection means a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode for imparting a second net deflection and a second net transverse velocity component to said beam transverse to said focusing field; and said first and second net deflections being in the same direction and said first and second net transverse velocity components being in opposite directions.
 5. Electron beam control apparatus for cathode ray tubes comprising: means providing a magnetic focusing field extending along the longitudinal axis of said tube, said focusing field causing said beam to form focus nodes and antinodes in its trajectory; first deflection means disposed along said longitudinal axis of said tube for imparting a first net deflectioN and a first net transverse velocity component to said beam transverse to said focusing; second deflection means disposed along said longitudinal axis displaced from said first deflection means a distance substantially equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode for imparting a second net deflection and a second net transverse velocity component to said beam transverse to said focusing field; and said first and second net deflections being in opposite directions and said first and second net transverse velocity components being in the same direction.
 6. Electron beam control apparatus for cathode ray tubes according to claim 4 wherein: said first deflection means includes at least one deflection electromagnet; and said second deflection means includes at least one deflection electromagnet.
 7. Electron beam control apparatus for cathode ray tubes according to claim 4 wherein: said first deflection means includes at least two electrostatic deflection plates; and said second deflection means includes at least two electrostatic deflection plates.
 8. Electron beam control apparatus for cathode ray tubes according to claim 5 wherein: said first deflection means includes at least one alignment electromagnet; and said second deflection means includes at least one alignment electromagnet.
 9. Electron beam control apparatus for cathode ray tubes according to claim 6 wherein: said first and second net deflections are of substantially equal magnitude; and said first and second net transverse velocity components are of substantially equal magnitude.
 10. Electron beam control apparatus for cathode ray tubes according to claim 7, wherein: said first and second net deflections are of substantially equal magnitude; and said first and second net transverse velocity components are of substantially equal magnitude.
 11. Electron beam control apparatus for cathode ray tubes according to claim 8, wherein: said first and second net deflections are of substantially equal magnitude; and said first and second net transverse velocity components are of substantially equal magnitude.
 12. A method of controlling the deflection of a magnetically focused electron beam in a cathode ray tube comprising: imparting a first net force to said electron beam over a first portion of its trajectory, said first force producing a first net deflection component and a first net transverse velocity component on said beam; imparting a second force to said electron beam over a second portion of its trajectory, said second force producing a second net deflection component and a second net transverse velocity component on said beam; and said first and second portions of said trajectory being displaced a distance equal to an odd multiple, including one, of the distance between a focus node and an adjacent focus antinode of said beam. 